A stereoscopic display system usually presents the two eyes of an observer with images with parallax from individual viewpoints. As methods of presenting the two eyes of the observer with images with parallax, there are two conventional methods: a method of using a pair of special spectacles; and a spectacleless method.
The method of using the spectacles switches right and left parallactic images, which are displayed alternately on a time division basis, in such a manner that the images reach the two eyes of the observer via the spectacles. Thus, to present the stereoscopic display to the observer, the observer must wear the spectacles, which involves an unpleasant and uncomfortable feeling.
On the other hand, the spectacleless method usually employs a lenticular lens or parallax barrier. In this method, a display system displays right and left parallactic images for each vertical pixel line, and has a lenticular lens or parallax barrier mounted in such a manner that the light rays emitting from the individual pixel lines are led to the two eyes of the observer. Thus, it must display the right and left parallactic images for each vertical pixel line of the display system. Accordingly, the pixels on a line of the display system is divided into right pixels and left pixels, thereby halving the number of pixels of the image. In addition, it is difficult for the lenticular lens system to switch between the presence and absence of the lenticular lens. Consequently, to display a plane image, the lenticular lens system must display different pixel lines to the two eyes as in the case of the stereoscopic image, thereby lowering the resolution of the plane image display. As for the parallax barrier system, it can eliminate the parallax barrier during the plane image display by configuring the parallax barrier by a liquid crystal device. Consequently, it can carry out the plane display at the original resolution of the display panel. However, since the parallax barrier system cuts off part of light rays from a light source with the parallax barrier during the stereoscopic display, it presents a problem of darkening the display.
As a method to circumvent the problem, a method is proposed which displays the right and left parallactic images on a transmissive display panel on a time division basis in the same manner as the method of using the spectacles, and switches the directivity of a light source that illuminates the display panel, thereby guiding the right and left parallactic images to the two eyes. For example, FIG. 22 shows a system proposed by Cambridge University. It comprises a transmissive display panel 4, a collimator lens 6 installed at its back, and a light source array 7 that is placed at its back and emits light successively. The light emitted from a light source cell 7a in the light source array passes through the collimator lens 6 disposed in front of the light source, and then through the transmissive display panel 4, and is converged with directivity. Accordingly, as for the image on the transmissive display panel, it is observable only in the converged direction. Thus, by switching the light-emitting cell of the light source array and the parallactic image displayed on the transmissive display panel in synchronization, the right and left parallactic images can be guided to the two eyes of the observer, thereby enabling the stereoscopic vision. The system using the light-emitting position control and the collimator lens can accurately convert the position of the light-emitting cell on the light source to the angle of illuminating light or to the visibility position through the collimator lens. As a result, the system can perform excellent directivity of the illuminating light, and hence can achieve high quality stereoscopic vision by good separation between right and left images.
As a method of downsizing the foregoing system, Japanese patent application laid-open Nos. 5-107663/1993 and 10-161061/1998 propose a method of dividing light rays from a light source into switchable stripe-like or matrix-like light sources by switchable shutter elements such as a liquid crystal device, and then achieving the directivity of the light source by a lenticular sheet which is placed in front of the light source and serves as a collimator lens. Although the method can carry out the stereoscopic display without lowering the resolution, it has a problem of decreasing light efficiency and darkening display because it cuts off part of the light rays from the light source to create the stripe-like light sources. In addition, since it requires expensive liquid crystal shutter elements in addition to the display panel to create the stripe-like light sources, it has a problem of being unable to implement a low-cost system.
FIG. 23 shows another method proposed in Japanese patent application laid-open No. 2001-66547. Instead of achieving the directivity of the light source by the collimator lens, the method combines two pairs of light sources 1a and 1b with backlight light guiding plates 2a and 2b, and switches the directivity of the illuminating light using light deflection effect by a prism sheet 8 disposed under a liquid crystal panel 4, thereby obviating the need for the expensive switchable shutter elements. Since the method controls the directivity of the illuminating light by only the adjustment of the light emitting luminous intensity distribution from the light guiding plates, it is more difficult for the method to obtain the sufficient directivity than the foregoing system that can determine the directivity of the illuminating light explicitly by the shutter elements and the collimator lens. An example of Japanese patent application laid-open No. 2001-66547 states that the angle of the light emitting from the light guiding plate has its peak at 70 degrees and is distributed from 60 to 80 degrees, the values are considered to vary to some extent depending on the shape of the light guiding plates and light producing structure. Thus, to achieve uniform brightness with maintaining the light emitted angle in that range, it is necessary to strictly limit the shape of the light guiding plates and their design. Thus, it has problems in that it easily brings about crosstalk between right and left because of the degradation in the directivity, and it must prepare two pairs of the light guiding plates as in the foregoing Japanese patent application laid-open No. 2001-66547 to obtain good luminous intensity distribution characteristics.
As described above, the conventional stereoscopic display systems have the following problems. First, the method of using the spectacles has inconvenience of wearing the spectacles. As for the spectacleless method, the method of using the lenticular or parallax barrier has a problem of decreasing the resolution of the stereoscopic image or plane image, or reducing the brightness. As for the conventional method of switching the directivity of light, the method of using the switching shutter elements and collimator lens is costly because it requires expensive switching shutter elements. The method of directly controlling the directivity of light by the light guiding plates has a problem of easily bringing about crosstalk between right and left because of the difficulty of controlling the directivity, and a problem of complicating the configuration and being expensive because it uses two pairs of the backlights.
The present invention is implemented to solve the foregoing problems. Therefore it is an object of the present invention to provide a display system capable of implementing high quality stereoscopic images with little crosstalk without decreasing the resolution of both the stereoscopic and plane images, and of achieving stereoscopic vision or displaying different frames simultaneously on the same screen without using the spectacles, which is simple, low cost and suitable for portable information terminals.